Rock drill cutting insert of hard metal



July 8, 1958 D. W.'HAGLUND Rocx DRILL. CUTTING INSERT oF HARD METAL Filed July 6, 1955 2 a j a g ad INVE TOR @N1 v v ATTORNEYS United. States Patenti() as y y 2,842,342 RoCK DRILL CUTTING INSERT oF HARD 'METAL Didrik Wilhelm Haglund, Sandviken, Sweden, assignor to Sandvikens Jemverks Aktiebolag, Sandviken, Sweden, a corporation of Sweden Application July 6, 1955, Serial No. 520,307

4 Claims. (Cl. Z55-63) This invention relates to rock ,drill cutting inserts formed of hard metal.

By hard metal is meant a sintered alloy consisting essentially of one or more carbides and/or other hard materials, for instance tungsten carbide, combined with one or`more bonding metals such as cobalt or other metals 'of the iron group.

from the cutting edge or toward the bottom of the insert.V

-fForbest performance-rock-drill cuttingtinserts must have a high resistance to wearas -wellas .a satisfactory mechanical strength-toughness-in order to avoid breaking and crumbling Vunder the `great shock strains which are'. applied. during boring with a modern percussion drilling machine. The cutting insert therefore in itself has to combine the highest 'possible resistance to wear and toughness.A 1

However, it is very difficult to 'combine' these two qualities in a hard metal cutting insert of the hornogeneous type, -by which is meant cutting inserts with uni form 'grain size and/'or chemical composition. Thus if hardness and consequently also resistance to wear is increased the'cutting insert becomes morebrittle, Vand converselyif the ltoughness and consequently the mechanical strength is increased the cuttingl -insert becomes less resistant to wear. t i Y 'l Therefore it has been suggested l'heretofore to produce hard' metal cutting inserts withAzonesfof1diiferentresistance to wear. The more wear resistant material is placed at thehe'nds of the cutting insert atAthe periphery of the drill'bit or in o'n'eor 'more' relatively thin zones arranged parlle'lwith the sidesurfaces of the cutting insert. The moreuwearzresistant material usuallyvhas a lower content ofbonding metal than the more tough one. Further it is known that. a -diifererrcein'resistance to wear may be accomplished through suitable choice of carbides or throughsuita'ble choice vof grain size in the hard metal. 4In comparison'withthe earlier known cutting inserts, both the homogeneous as well as those of the compound type, thecutting insert according to the present invention gives a substantially increased resistance to wear and strength.

The invention is based upon the following considerations. If the cutting insert consists of a hard, highly wear resistant hard metal its remaining height after a certain number of bore meters is greater than that of a cutting insert with a less wear resistant, tougher hard metal. In other words the tough material wears away faster than the harder material. The tougher cutting insert may, however, be worn down to a lower insert height than the harder and more wear resistant insert vchanical stresses.

is used more and more as the insert height approaches the zone of -danger of breakage on account of the me- A further advantage to the invention is that the position of the more wear resistant hard metal prevents the formation of aY-,so-called counter peg at the periphery of the drill bit.y Such a counter peg is usually formed in certain species of rock and not only prevents the advance of the drill bit but also frequently causes breakage of the cuttinginserts. l Variations in resistance to wear andY toughness for the ditferent zones in the cutting insert according to thein, Vention may be obtained in a known manner, either'by a variation in grain size or by a variation in analysis or by -a simultaneous variation iboth in grain size and analysis. At the same analysis the more fine-grained material usually rforms the more wear resistant harder zone or zones -while the lmore coarse-grained material provides the tougher zone or'zones.VK Y r The invention will now be further described in con.- nection with the accompanying drawings which show a number of embodiments of cutting inserts in accordance with the invention. .Fig i1 is a perspectiveview of a rock drill bit provided with ahard metal cuttingfinsert;

Figs. 2 and 3 are side and end views respectively of a cutting insert;

Figs. 1-14 show different embodiments in cross-section on the line A-A in Fig. 2; and Y Figs. 15-17 and Figs. 18'-20 show different embodiments in longitudinal section along the line B-B of Fig. 2 and the line C-C of Fig. 8 respectively.

The drill bit 10 shown in Fig. l is provided with a hard metal insert 11 fastened into a groove by means of brazing or in any other suitable way. The drill bit may be provided with more cutting inserts, for examplewfour inserts arranged in cross-form, and the cutting inserts may be divided yinto two or"more separate 'parts as is well vknown inthe art. The invention is not limited to the plate-like form of the cutting nsert,`shown in Fig. l, which insert may have any other known form' within the scope'-of'the appended claims. Thus 'the cutting insert may-have converging sidesurfaces in boring direction. ln" all of the embodiments illustrated 12 is the more wea'l resistant and usually yalso the' harder part andl isthetougher part. vIn Figs., 4"-14, whichshowgsections perpendicularl `to `the longer 'axis of' vthe Vcutting insert l illustrate several different ways in which the hard metal zonesmayrhe. arranged. According to, Fissa-,1.0 the morewearresistant hard metal 12 is substantiallyweglge shaped with the side boundaries converging downwardly toward the base of the insert. The side boundaries of the wedge-shaped portion are completely surrounded by the tougher hard metal. Figs. 1l-14 on the other hand show the tougher portion wedge-shaped with the side walls converging upwardly toward the cutting edge -of the insert and embedded in the more wear resistant portion. As appears in all of the figures the major part of the cutting edge of the insert is formed by the more Wear resistant part of the insert. This more wear resistant part of the insert may extend down to the bottom of the insert where the major part of the insert consists of tougher material (Figs. 4-7, and 9 and 12) `or terminate at a substantial distance above the bottom of the insert (Figs.

nPatented VJuly 8, 1958 Y 'of the cutting insert according Y 8, 10, 11, 13 and 14). The more wear resistant as Well as the tougher portions of the insert may terminate in an edge (Figs. 5, 6 and l2) or may be more or less blunt for example` of a blunt or rounded form (Figs. 4, 7, 1l,

13 and 14). .Further it may be advantageous to provide- By choosing a suitable grain size and/or analysis forl the different zones of the insert the desired qualities of great wear resistance in the upper part anda good toughness in its below part may be provided. Usually the cutting insert consists of a sintered unit -and the boundaries between the zones may be sharply defined or they may show a more or less continuous mergence. It is also possible to manufacture the different zones separately and then unite them in a suitable way, for instance by brazing.

As an example of different grain sizes in the different zones of a cutting insert with substantially the same analysis throughout, the grain size for the more wear resistant zone or zones may be between 1 and 2..to 2.5 microns and for the tougher zone or zones between 3 and 6 microns or 4-5 microns. In this example the composition may be 9l94%, preferably 93% WC, and 6-9% preferably 7% of Co. As mentioned above the difference in resistance to wear and toughness may also be provided for by selection of the composition, for example the cobalt content, which for the more wear resistant zone may be chosen for instance between 5 and 9% and for the tougher zone for instance between l and 15%. This variation in composition may be combined with variation in grain size. g

Figs. 15-17 show a section in the longitudinal direction of the cutting insert parallel with the bottom surface, which is indicated by the line B-B in Fig. 2. As appears from these figures the more wear resistant zone or zones 12 extend to the end surfaces of the cutting'insert and may either extend along the whole length of the cutting insert (Fig. l) or may be divided into two or more zones in the longitudinal direction of the cutting insert, separated by tougher hard metal 13 as shown in Figs. 16 and 17. The tougher hard metal may form the bottom layer as well as the central part of the cutting-insert. Figs. 18-20 show alternative embodiments of the cutting insert in accordance with the invention seen vin a longitudinal section along the line C-C of Fig. 8. The lower boundary of the more wear resistant zone orzon'esmay be parallel with the bottom of the insert (Fig. 18),.upwardly convex as shown in Fig. 19, angular as shown in Fig. 20 or polygonal.

In comparison with earlier used cutting inserts the inserts according to the invention give a very high resistance v2,842,342 Y Y m j In Figs. 2 and 6 the dotted lines n n, b-b and c--c show different stages of the wearing down of the cutting insert. It appears from these lines how the ratio between the tougher and the more wear resistant zones increases as the cutting insert is worn down but the cutting edge during the whole wearing down period consists of the more wear resistant hard metal. When the height of the insert has been reduced to the point where there is a risk of breakage on account of the mechanical stresses the remaining part of the cutting insert substantially consists of the tougher material. In comparison with earlier cutting inserts this point at which the insert must be discarded due to danger of breakage is considerably lower. As an example may be mentioned that the cutting height for the normally used cutting inserts in drilling a certain kind of rock is l0 to l5 mm. whereas the cutting inserts according to the invention may be worn down t0 about 3 to 5 mm. i

The invention is not limited to the described and shown embodiments but embraces every rock drill cutting insert within the scope of the following claims.

I claim:

l. A rock drill cutting insert having a cutting edge surface, a plane bottom surface opposite to said cutting edge surface, oppositely disposed substantially parallel plane side surfaces and oppositely disposed end surfaces, said insert consisting of at least one zone of hard metal which has a relatively greater resistance to wear and at least one zone which has a relatively greater toughness,rsaid zone which has a relatively greater'resistance to wear constituting substantially the whole of said cutting edge surface and extending downwardly therefrom with a decreasing crosssectional area in the direction from said cutting edge surface toward said bottom surface, said zone which hase relatively greater toughness constituting the remainder of the insert and extending upwardly with a decreasing cross sectional area in the direction from said bottomsurface towardV said cutting edge surface, the lateral boundary surfaces between said zones being substantially plane surfaces and lying at acute angles to the adjacent side surfaces of said insert.

2. Rock drill cutting insert according to claim 1, characterized in that the zone of greater toughness successively increases in vcross sectional area in at least a substantial to wear during the whole useful life and they can be worn down considerably thinner than has hitherto been possible. The result is a considerably increased amount of drilling per bit.

part of the insert in the direction from the cutting edge surface towards said bottom surface.

3. Rock drill cutting insert according to claim 1, lcharacterized in that said boundary surfaces are inclined toward each other with an angle `between the surfaces of more than 20. i 4. Rock drill cutting insert according to claim 3, characterized in that at least one of said zones tapers to an edgelike configuration.

References Cited in the le of this patent UNITED STATES PATENTS 2,582,231 Catallo Jan. 15;i 1952 FOREIGN PATENTS 284,747 Switzerland Nov. 17, 1952 683,018 Great Britain Nov. 19, 1952 

